TRICARBONYL(ETA-6-HEXACHLOROBENZENE)CHROMIUM(0)

Lithiation of (eta6-C6H5Cl)(Cr(CO)3(1) with n-butyllithium in tetrahyd rofuran at-78-degrees-C followed by chlorination of the intermediate l ithioarene complex with hexachloroethane afforded primarily (eta6-1,2- C6H4Cl2)Cr(CO)3 (2) and significant amounts of four new substances: (e ta6-1,2,3-C6H3-Cl3)Cr(CO)3 (3), (eta6-1,2,3,4-C6H2Cl4)Cr(CO)3 (4), (et a6-C6HCl5) Cr(CO)3 (5), and (eta6-C6Cl6)Cr(CO)3 (6). Regioisomers of 2 -4 were not observed. The wavenumber of the symmetric CO stretch (nu(C O)A, determined by infrared spectroscopy) and the oxidation potential (E-degrees' determined by cyclic voltammetry) increased regularly with the increasing number of chloro substituents. Crystalline 6 was struc turally characterized by X-ray diffractometry: triclinic, P1BAR, a = 7 .538(2) angstrom, b = 7.734(3) angstrom, c = 13.511(3) angstrom, alpha = 75.26(2)-degrees, beta = 74.48(2)-degrees, gamma = 60.940, V = 656. 1(8) angstrom3, Z = 2, R = 0.053, R(w) = 0.069. Noteworthy in 6 is the short chromium to C6 centroid distance of 1.680(1) angstrom. Infrared spectroscopic, electrochemical, and metrical data for 6 lead to the c onclusion that hexachlorobenzene is the most electron-poor arene thus far coordinated to a Cr(CO)3 fragment.